What is sound? It is a pressure wave. So long as you have some kind of gaseous medium, you will have the possibility of forming pressure waves in it by "shocking" it in some way. In space, the interplanetary medium is a very dilute gas at a density of about 10 atoms per cubic centimeter, and the speed of sound in this medium is about 300 kilometers per second. Typical disturbances due to solar storms and "magneto-sonic turbulence" at the Earth's magnetopause have scales of hundreds of kilometers, so the acoustic wavelengths are enormous. Human ears would never hear them, but we can technologically detect these pressure changes and play them back for our ears to hear by electronically compressing them.

Now that we are intrigued, we've sent a tweet to Colonel Hadfield asking for his favourite sounds in space and while we await his response, check out our top 10 list of space sounds, which includes some historic moments as well as pop-culture favourites inspired by the great beyond.

1. Neil Armstrong's moon landing.On July 20, 1969, Neil Armstrong uttered the immortal words, "That's one small step for a man, one giant leap for mankind." Humanity hasn't been the same since.

2. "The Imperial March." Darth Vader's theme song is not only popular with Star Wars fans, it's an ageless classic that makes us think immediately of the galaxy and what might not be so far, far away.

3. Mark Kelly's emotional speech to his wife. "I'm looking forward to coming home. Tell my wife I love her very much, she knows," were among the words U.S. astronaut Kelly recorded from the International Space Station in the months following the attempted assassination of his wife, Congresswoman Gabrielle Giffords of Arizona. Kelly's message was played during U2 concerts in 2011. He was on a space shuttle mission while Giffords recovered from the shooting.

4. "The Final Frontier." For multiple generations, the voice of Star Trek captains speaking the monologue associated with that sci-fi franchise's films and TV shows has inspired many to want to explore space.

5. Chris Hadfield's performance with Barenaked Ladies. On February 8, 2013, Hadfield teamed with one of Canada's favourite rock groups, Barenaked Ladies, on "I.S.S. (Is Somebody Singing)," a song that was commissioned by the CBC. It was written by Hadfield and Robertson, and partially recorded in space.

6. Theme song from "Close Encounters of the Third Kind." The thrilling 1977 movie features a theme song built around five key notes. In the film, those notes are used by aliens to communicate with humans.

7. Mars Curiosity Rover's spooky landing. In August 2012, the European Space Agency's rover hit the surface of Mars and did so with a loud and eerie whoosh that could have been a score for any sci-fi horror flick set in space.

8. "E.T. phone home." Steven Spielberg tugged at our heart strings in 1982 with an adorable alien with a squeaky voice who came from outer space to remind us all of the importance of home.

9. Felix Baumgartner's free fall. In 2012, the Austrian daredevil completed athrilling jump from 128,000 feet above the earth. While Baumgartner wasn't miked during the fall itself, we could hear the instructions being given to him from a member of his team on the ground. The calm, detailed instructions as he manoeuvred out of the capsule and steadied himself to jump was nerve-wracking — and unforgettable.

10. "Superman." Conductor John Williams wrote the theme song for the 1978 movie and it has remained a timeless piece of music that evokes the mythology surrounding one of the greatest comic book heroes of all time — and perhaps the most famous fictional space alien in history.

Getting back to the actual sounds of space here is a video we found very interesting:

Be sure to let us know your favourite space sounds. Also, if you have a hearing-related question, don't be shy about asking. Send your comments and questions to the Connect Hearing Facebook page at facebook.com/ConnectHearingCanada.